Process for treating hydrocarbons



March 25, w41. w. B. LERCH Erm.

PROCESS FOR TREATING HYDROCARBONS Filed June 20, v1938 E ww:

Patented Mar. 25, 1941 PROCESS FOR TREATING HYDROC 'lli'l william Bruce uren, Clyde n. Mathis, and Eugene J. Gatchell, Bartlesville, Oklai, assignors to Phillips Petroleum Company, a corporation oi Delaware Appncsuon'rune zo, 193s, serial No.' zum 8 Claims.

This invention relates to the use of cyanamide compounds for the removal of hydrogen sulde and for other objectionable sulphur compounds, mercaptans, etc. from gaseous or liquid hydrocarbons. The invention` further relates to the process of using the hydrogen sulde and objectionable sulphur compounds present in the gaseous or liquid hydrocarbons to react with a cy- -anamide compound to form thiourea and isothiourea ethers.

Gaseous or liquid hydrocarbons, particularly crude gasoline contain appreciable quantities of sulphur compounds, as mercaptans, and it is the usual practice to remove them or convert them to harmless compounds by an appropriate chemical treatment. This process is referred to among oil technologists as sweetening A sweetened gasoline is sweet to the doctor test. That is, it shows no discolprization when treated with alkaline sodium plumbite and sulphur.

'I'he improved method of rening petroleum hydrocarbon products herein set forth is of special value and application in the treatment of light petroleum distillate such as natural gasoline. refinery straight run and cracked gasolines, kerosenes, petroleum solvent naphthas, liqueed petroleum gases, and the like. Such unrened petroleum products contain mercaptans which give the products undesirable odors and render them corrosive and unstable. Petroleum hydrocarbon products containing mercaptans are commonly termed soun Conversion of these mercaptans partially or entirely to disuldes, or completely removing them, is usually termed sweetening Customarily, these sour compounds are altered, or removed by chemical treatment of the sour hydrocarbon uid with alkali plumbite and sulphur. In some instances, particularly with natural gasoline sweetening is accomplished with alkaline hypochlorite solution but like the alkali plumbite method, this method has proved to be not only uneconomical and cumbersome but also has been found to introduce undesirable constituents into the products -being sweetened, such constituents in many instances of high mercaptan content products being as detrimental to the petroleum products treated as those present originally'. Still other methods have been suggested for the removal or conversion of mercaptans but in nearly every instance these methods involve numerous treating steps, requiring close control, so that the increase in operating costs renders them uneconomical.

An object of the present invention is to pro- (ol. 19e-ao) vide al process bywhich Vthe sour compounds in sour oils, distillates or gas may be removed orl altered, or converted into compounds which are not` sour, thus rendering the sour loils,'distil lates or gases sweet, and'in which process, if desired, the agent or agents employed to sweeten the sour oils, distillates or gases may be reactivated or regenerated concurrently with their use in the sweetening of the sour oils, distillates or gases, whereby the sweeteningvof the sour oils, distillates or gases and the maintenance of thel activity of said agent or agents may be eiecte'd at the same time.

A `further object of the invention is the provision of a process by which sour oils, distillates, or gases, may be sweetened without the use of the so-called doctor solution, that is an aqueous solution of sodium plumbite and also without the use ofl aqueous solutions of salts of metals forming insoluble sulides with hydrogen suliide, such as aqueous solutions of cupric chloride or other cupric salts.

A still further object of the invention is to provide a process in which, if desired, the spent agent or agents employed to sweeten the sour oils, distillates or gases may be processed to Secure a thiourea solution instead ofreactivating the same for use in sweetening the sour oil, distillate or gases.

A still further object of the invention is to provide a process in which, if desired, the spent agent or agents employed to sweeten the sour oils, distillates or gases may be acidiiied and then processed to secure thiourea crystals.

Other objects and advantages along with the foregoing will be apparent to those skilled in the -art to which the present invention pertains from the disclosure thereof hereinafter set forth, and' are attained bythe invention described in detail below.

In the accompanying drawing we have shown diagrammatically certain kinds of apparatus which maybe used in carrying out the treatment, but it is to be understood that the invention is in no sense restricted to these particular types of apparatus.

' l Figure i vshows a diagrammatic view of one modication of the process wherein the sweetening process has regenerative apparatus for the spent agent or agents,

Figure 2 shows a diagrammatic view of another modliicationof the process wherein the sweeteningmrocess 'is connected with apparatus to'process the spent agent -or agents so as to recover a thiourea solution,

Figure 3 shows a diagrammatic view of another modication of the process wherein the/ sweetening process is connected with apparatus to process the spent agent or agents with an 5 acid so as to recover thiourea crystals and a filtrate.

Calcium cyanamide or any cyanamide compound will remove mercaptans from hydrocarbons as well as removing the hydrogen sulfide. The cyanamide and mercaptan react to form isothiourea ethers which are quite insoluble in the solvents present.

Referring more particularly to Figure 1, which constitutes a proposed showing of apparatus for the preferred modication of the process for the Vremoval of hydrogen sulfide from gases by the use of commercial calcium cyanamide,"l represents a mixing tank wherein calcium cyanamide from line 2 is mixed or dissolved in water from line 3. It is essential that the temperature in the mixing tank be kept below C. throughout the mixing. From the mixing tank I, the suspension passes through the filter 4 where it is filtered and the filtrate containing the calcium cyanamide is fed continuously into the top of the scrubber tower 1 from storage tank 5 by means of pump i. It is to be noted that sulphur, thio.- urea, ammonia or other amines may be added as a catalyst to the calcium cyanamide solution when the same is in the 4storage tank 5. The raw gas, enters the scrubber tower 1 at the bottom thereof through the line 8 and the purliied product leaves at the top through line 9. The raw gas, inpassing up through the scrubber tower 1, is continuously being subjected to the calcium cyanamide solution, and the hydrogen sulfide reacts with the calcium cyanamide lsolution to change the composition of the same and allow a puried product to leave thel scrubber tower through the line 9. The spent scrubber solution leaves the bottom of the tower 1 through the line I0. This spent scrubber solution contains thiourea, calcium sulfhydrate and a precipitate of .calcium carbonate forgmed' from the calcium cyanamide and carbon dioxide contained in most natural gas.

'I'he spent lscrubber solution can be treated by three diiierent methods lafter it leaves the tower and the iirstego b /dis'cussed will be that portion on'the right of gure 1. The spent scrubber solution passes from the line I0 to the line II into iilter l2 from where it is pumped into regenerator I3. Steam is entering the bottom o f, regenerator I3 through the line I4 and supplies heat to the solution in regenerator I3. In the regenerator I3, the calcium sulfhydrate is,broken down into calcium hydroxide and hydrogen sulde by heating. When the thiourea is heated in the presence of catalysts such as mercurio chloride,

lead peroxide, mercuric oxide or lead hydroxide,

it loses-hydrogen sulfide and yields cyanamide. Sufficient catalyst is present at all times in the regenerator I3 to allow these reactions to pro-I ceed to completion. Cyanamide and calcium hydroxide react to form calcium cyanamide and water, the starting substance, which leaves the regenerator at the top thereof by line I5, passes through cooler I8 and is placed in the storage tank 5 through line, I1 to be recirculated throughthe scrubber tank 1. The hydrogen sulfide. gasl leaves the top of the regenerator tank I3 through the line I4 and may be disposedof in any way. desirable. By this method it is necessary to add, only enough calcium cyanamide to compensate u for mechanical losses. The theoretical reactioninvolved in this process 'is illustrated in the following chemical equations: ca(sH).+neat (stglmg=ca(on +2H1S Calcium sulihydrate cxum hydroxide Hydrogen sulfide osmmm-heat (steam-teammate CN-N1I1 Thiourea Hydrogen sulfide Cyanamide c(oH`),+oNNH,=2H,o +CacNr Calcium hydroxide Cyanamide Watery Calcium cyanamille "It passes to filter I9 where the solution is ltered and thence to evaporator 20 where some of the liquid is evaporated oir. The steps under this process are carried out preferably under reduced pressure and the evaporation proceeds until the thiourea reaches concentration suitable for use in making synthetic resins and is stored in tank 2l. If the line II is completely closed, by this method there is no recycling of the spent material, instead it is used as a raw material for the manufacture of resins or other purposes for which it is applicable.

Referring to the process shown in Figure 3, the spent scrubber solution may pass from -line I0 to line 22 or the solution may be divided in any proportions desired between the other two lines, and passed to the mixer tank 23. ,Connecting into tank 23 is the line 24 which delivers a dilute sulphuric acid or any other acid to the tank and mixes the same with the spent scrubber solution to acid'ify the same and the whole is cooled. If desired, in place of the dilute sulphuric acid, the carbon dioxide from the flue gases .may be used where such is available. Hydrogen sulfide is driven oil from the spent scrubber solution and the residue goes to the filter 23. The filtrate is evaporated in evaporator 21 from where the fluid passes to crystallizing tank 23. The solution then passes to lter 23 where the thiourea crystals are removed from the lter and the filtrate is pumped back to mixing tank I through pipe 30 where it dissolves .more crude calciumA cyanamide 'or if desired may be discarded.

*This process of removing hydrogen sulfide is continuous by. any of the methods described. It may be a method of removing hydrogen sulfide in which only enough fresh chemical for makeup is required, or it may be a method of removing hydrogen sulfide from gas which yields a source of thiourea for industrial purposes. It is to be understood that while sour gas has been used to illustrateV the apparatus shown in the drawing.

similar setups could be used for sweetening other sour hydrocarbons and it is not to be understood that the process is limited only to gas.

- It is not essential to have a complete plant as just described but a suspension of calcium cyanamide in a tower equipped with proper agitation affords an eiiicient method of hydrogen sulfide removal, however, the recovery of thiourea is more diflicult. Calcium cyanamide, for instance, may be used dry, as a paste, or a suspension in a solvent such as water to remove hydrogen sulfide from hydrocarbons such as natural gas, coal ga's, producer gas, water gas, refinery still gas, or liquid hydrocarbons such as crude oil or thel fractions obtained therefrom or any gases or liquid materials containing hydrogen sulfide.

We prefer to use calcium cyanamide because of its availability and low cost but do not limit ourselves to this compound since cyanamide, sodium cyanamide or other cyanamide salts may be used equally as well and are to be considered within the scope of this invention. In practice the gas or hydrocarbon vapor, for instance natural gas, containing hydrogen sulde is conduct-v ed through a bed of dry calcium cyanamide or is scrubbed with a solution or suspension of calcium cyanamide in water or other solvent in the conventional countercurrent type of scrubber. 'Ihe theoretical reaction involved is illustrated in the following chemical equation:

`CaCNz 3R18 Ca(SH)g CS(NH2) Calcium Hydrogen Calcium Thiourea. cyanamide sulfide sulihydrate According to this equation, one weight equivalent, for instance pounds, of calcium cyanamide should react with three weight equivalents or 102 pounds of hydrogen sulfide to form as one of the products of the reaction one weight equivalent or '76 pounds of thiourea which may be separated as a valuable by-product. In practice it has been found that a much greater weight of hydrogen sulde is required to react with the same weight of calcium cyanamide which would indicate that the reaction is morecomplex than that indicated by the chemical equation asgiven.

This process has several-advantages over the well-known method of circulation "of a solution of caustic soda or sodium hydroxide for the removal of hydrogen sulde. 'I'he calcium cyanamide is cheaper than caustic soda and pound for pound it has a. much greater capacity for absorbing hydrogen sulfide. Thus theoretically one pound of caustic soda will unite with 0.85 pound of hydrogen sulde according to the equation:

NaOH lHis Nais H10 Sodium Hydrogen Sodium Water hydroxide sulfide sulilde In practice it has been found that one pound of commercial calcium cyanamide will unite with 2.3 pounds of hydrogen sulfide.

If desired, it is not necessary. to have the calcium cyanamide in solution with water but the same may be used in a dry state. Dry granular calcium cyanamide may be packed in an upright cylindrical tank which should be equipped with coils cooled by circulating water to maintain the temperature below 100 F. and the gas containing hydrogen sulde is passed upwardly through the tank. The gas contacts the calcium cyanamide and the hydrogen sulfide is absorbed rapidly with the process continuing until the eilluent gas shows traces of hydrogen sulde when the flow of gas is switched to another similar absorber while the spent calcium cyanamide in the rst cylinder is extracted with solvents to remove the thiourea after which the absorber is ,cleaned and recharged with a fresh batch of calcium cyanamide and is ready for a new cycle of operation. In treating gasoline or kerosene to remove f the sulphur compounds, this treatment may be applied by passing the vapors over a bed of cal- 5 cium cyanamide or cyanamide.

From the foregoing it is believed that the steps and advantages of the process may be readily understood by those skilled in the art and it is manifest that changes may be made in the details disclosed without departing from the spirit of the invention, as expressed in the claims. In the appended claims, we mean the term hydrocarbons"` to generically define gasoline, kerosene, and other petroleum distillates and oils.

Having thus described our invention, what We claim is:

1. The process of removing sulphur compounds from hydrocarbons which comprises passing said hydrocarbons through a bed of dry cyanamide.

2. The process of removing sulphur compounds from hydrocarbons which comprises passing said hydrocarbons through an aqueous cyanamide solution.

3. The process of removing sulphur compounds from hydrocarbons which .comprises passing said hydrocarbons through a bed of dry cyanamide compound.

4. The process of removing sulphur compounds from hydrocarbons which comprises passing said hydrocarbons through an aqueous cyanamide compound solution.

5. The process of removing sulphur compounds from hydrocarbons which comprisesv passing said hydrocarbons through a bed of dry calcium cyanamide.

6. 'I'he process of removing sulphur compounds from `hydrocarbons which comprises passing .said hydrocarbons through an aqueous calcium cyanamide solution.

7. The process of sweetening hydrocarbons which comprises treating said hydrocarbons with calcium cyanamide in a scrubber tower, conducting the spent scrubber solution to a regenerator to reconvert the spent solution to calcium cyanamide and then recirculating the regenerated calcium cyanamide solution through the scrubber tower. y

8. The proces-s of sweetening hydrocarbons which comprises treating said hydrocarbons with calcium cyanamide in a. scrubber tower conducting the spent scrubber solution to a regenerator where it is reconverted to calcium cyanamide solution inthe presence of a catalyst and steam and then recirculating the regenerated calcium'5.

cyanamide solution through the scrubber tower. 

